The present application claims priority to Japanese Application No. P11-312719 filed Nov. 2, 1999, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a production method of and an production apparatus for an optical recording disc comprising two round substrates bonded with each other.
2. Description of the Related Art
With reference to FIGS. 1A to 1E, a conventional production method of an optical recording disc will be explained. As shown in FIG. 1A, a second round substrate having 120 mm in diameter (made from, for example, polycarbonate) D2 is prepared. h2 is the center hole of the second round substrate D2. r2 is the recording surface of the second round substrate D2, with a data recording trace (comprising pit rows with different lengths and widths) formed concentrically or along a track tantamount to a circle.
As shown in FIG. 1B, an ultraviolet ray curing type resin R as an adhesive is dropped onto the recording surface r2 while rotating the second round recording plate D2 at an adequate position in the range of 15 mm to 50 mm in radius on the recording surface r2 of the second round recording plate D2 so as to apply the ultraviolet ray curing type resin R like a ring with a predetermined width substantially concentric with the second round substrate D2.
As shown in FIG. 1C, a first round substrate having a 120 mm diameter (made from, for example, polycarbonate) D1 is prepared. h1 is the center hole of the first round substrate D1. r1 is the recording surface of the first round substrate D1, with a data recording trace (comprising pit rows with different lengths and widths) formed concentrically or along a track tantamount to a circle.
As shown in FIG. 1D, the recording surfaces r1, r2 of the first and second substrates D1, D2 are superimposed via the ultraviolet ray curing type resin R for uncured bonding so as to obtain an optical recording disc. The optical recording disc obtained by the uncured bonding is rotated at a high speed so as to spread the ultraviolet ray curing type resin R between the first and second round substrates D1, D2 to the whole portion of the inner peripheral part and the outer peripheral part by the centrifugal force so as to have an even thickness to thereby obtain an optical recording disc D by the uncured bonding.
As shown in FIG. 1E, by irradiating an ultraviolet ray to the optical recording disc D comprising the first and second round substrates D1, D2 obtained by the uncured bonding via the ultraviolet ray curing type resin R spread in FIG. 6D for curing the ultraviolet ray curing type resin R, the first and second round substrates D1, D2 are bonded so as to provide a completed optical recording disc D.
According to the conventional production method of an optical recording disc, due to the irregularity of the wettability of the first and second round substrates with respect to the ultraviolet ray curing type resin, irregularity is generated in the spread of the ultraviolet ray curing type resin so that the ultraviolet ray curing type resin cannot be spread substantially concentric to the inner peripheral side like the first and second round substrates. Therefore, the inner peripheral side rim part of the cured ultraviolet ray curing type resin between the first and second round substrates cannot provide a beautiful outline shape substantially concentrically with the first and second round substrates, and thus an optical recording disc with a good quality has not been obtained.
Moreover, according to the conventional production method of an optical recording disc, the first and second round substrates are bonded via the ultraviolet ray curing type resin by the uncured bonding, and the disc obtained by the uncured bonding is rotated at a high speed so as to have the film thickness of the uncured ultraviolet ray curing type resin at a predetermined value. However, due to the irregularity of the wettability of the first and second round substrates with respect to the ultraviolet ray curing type resin, difficulty in controlling the centrifugal force applied on the uncured ultraviolet ray curing type resin, the irregularity of the plate thickness of the first and second round substrates, or the like, it has been difficult to obtain an optical recording disc with an even cured ultraviolet ray curing type resin film thickness between the first and second round substrate and a good quality.
Furthermore, among digital video discs (DVD) as one of the conventional optical recording discs, there are DVDs having a standard of a 20 xcexcm or less film thickness of the cured ultraviolet ray curing type resin between the first and second round substrates. According to the conventional production method for an optical recording disc, it has been extremely difficult to obtain a DVD with a 20 xcexcm or less film thickness of the cured ultraviolet ray curing type resin.
The prevent invention is to propose a production method and a production apparatus for an optical recording disc, capable of achieving a beautiful outline shape of the inner peripheral part side rim part of the cured ultraviolet ray curing type resin substantially concentrically with the first and second round substrates by spreading substantially concentric the ultraviolet ray curing type resin to the inner peripheral side like the first and second round substrates even in the case there is irregularity of the wettability of the first and second round substrates with respect to the ultraviolet ray curing type resin, and capable of obtaining an optical recording disc with a good quality by providing a even film thickness of the cured ultraviolet ray curing type resin with the film thickness controlled to a predetermined value or less even in the case there are irregularity of the wettability of both round substrates with respect to the ultraviolet ray curing type resin, difficulty in controlling the centrifugal force applied on the uncured ultraviolet ray curing type resin, irregularity of the plate thickness of the first and second round substrates, or the like.
A production of an optical recording disc according to a first aspect of the present invention comprises the steps of forming a layer of the ultraviolet ray curing type resin having a predetermined even thickness spread by rotating either one of the first and second round substrates at a low speed with the other one fixed while applying pressure on the first and second round substrates of an optical recording disc provided by uncured bonding of ring-like ultraviolet ray curing type resin disposed between first and second round substrates substantially concentrically with the first and second round substrates, rotating the optical recording disc provided by the uncured bonding, having the layer-like ultraviolet ray curing type resin with the predetermined even thickness, and irradiating an ultraviolet ray to the optical recording disc provided by the uncured bonding rotated at the high speed for curing the layer-like ultraviolet ray curing type resin so as to obtain a completed optical recording disc with the first and second round substrates attached.
According to the first aspect of the invention, a completed optical recording disc with the first and second round substrates attached is obtained by forming a layer of the ultraviolet ray curing type resin having a predetermined even thickness with the spread thereof by rotating either one of the first and second round substrates at a low speed with the other one fixed while applying pressure on the first and second round substrates of an optical recording disc provided by uncured bonding of a ring-like ultraviolet ray curing type resin disposed between first and second round substrates substantially concentrically with the first and second round substrates, rotating the optical recording disc provided by the uncured bonding, having the layer-like ultraviolet ray curing type resin with the predetermined even thickness, and irradiating an ultraviolet ray to the optical recording disc provided by the uncured bonding rotated at the high speed for curing the layer-like ultraviolet ray curing type resin.